Poor cold Idle / hard starting

I've got a 1976 KZ750b. I rebuilt the pair of Mikuni BS38's, synched the butterflys, adjusted the pilot jets to factory spec and replaced the rubber manifolds. I have good compression (not great but within factory spec), replaced the head gasket and valve seals, lapped the valves and did the WG coil mod. Timing is good when idling and the bike runs great when its warm but it still doesn't like to start/idle when its cold. I have a pair of inline fuel filters and the bowls and jets are clean so the carbs aren't clogged up.

I live in metro Detroit so its in the high 60's to low 70's right now but this was happening last year when it was super warm out too and a month ago when it was quite a bit colder.

When I go to start the bike, I open the petcock, pull up on the choke lever, and hit the start button. The bike will chug for a couple of seconds and if i give it a tiny bit of throttle it will start. If I let off the throttle it will idle really rough for a second or two and then die. If i immediately remove the choke while holding the throttle open a bit the engine will improve but still die if I let off the gas. I have taken to just turning up the idle screw until it idles happily, usually 1000-1100rpm and then turning it back down once it warms up.

It is easier to start when its choked so I know the choke is doing something but im not quite sure what.

I have tried adjusting the jets but it doesn't seem to be getting me anywhere. I am going through things in the FSM one by one but I was hoping someone would have some experienced insight.

Are the stock air box and filter attached to the carbs? Ed

Yup.

If so equipped, are the pilot jet plugs present, fitted properly, and in good condition?

Good Fortune!

I don't believe I have pilot jet plugs. Not exactly sure what they are.

Good Fortune!

Is that supposed to clean it out? Or tell me if I need plugs?

it tells you where your pilot jets are.

bvallerand wrote: I don't believe I have pilot jet plugs. Not exactly sure what they are.

Review of the carb parts diagram at kawasaki.com confirms your belief that the carbs at hand are the version without pilot jet plugs.

Information on kawasaki.com includes parts diagrams, part names, part numbers, models sharing same part, availability, etc. If needed, here's a link for help with navigating kawasaki.com and finding information.

www.kzrider.com/forum/13-bike-related/37...imitstart=0&start=20

Good Fortune!

My GPz was hard to start when cold and would idle horribly. I had to keep goosing the throttle to keep it from dying at stoplights until it had gone 3 miles or so . Then I adjusted the valves and all those cold start / bad idle problems went away. It really was night and day
Something to think about...

By adjusted the valves are you talking about adjusting the valve lash/ changing the valve shims?

bvallerand wrote: By adjusted the valves are you talking about adjusting the valve lash/ changing the valve shims?

Valve clearances are first measured with a thickness (feeler) gauge to determine whether the clearance of each valve is within specs.
Measuring is a routine scheduled maintenance item. And is usually a simple, quick, easy and relatively fool-proof procedure.

If all the clearances are found to already be within specs, then "adjustment" (adjusting the valve lash/ changing the valve shims) isn't needed.

On engines having exposed shims on top of the buckets (cam lobes in direct contact with the shims), "adjustment," when needed, is also usually a simple, quick, easy and relatively fool-proof procedure. A special tool is used to provide space between the cam and shim to allow removal and replacement of the shim. Removal and replacement of the camshafts isn't required.

On engines having hidden shims under the buckets (cam lobes in direct contact with the buckets), adjustment, when needed, is more complex, and not quite so fool-proof. Due to the additional procedures involved with removing and replacing the camshafts, with the attendant risks of stripping the cam-cap screw holes, and assuring correct cam timing upon re-assembly.

Good Fortune!